1. Field of the Invention
The present invention relates generally to internal combustion engines and more particularly to an arrangement for recirculating the exhaust gases of internal combustion engines within which a valve controlled by means of the vacuum within the intake manifold of the engine permits the diversion, depending upon the engine speed and load, of a predetermined amount of the exhaust gases to the inlet manifold so as to be recycled therewithin.
2. Description of the Prior Art
As is known, nitrogen oxides are among the pollutants emitted within the exhaust gases of internal combustion engines and it is also known that in recycling some of the exhaust gases with the fresh mixture entering the engine's inlet manifold the temperature of combustion within the cylinders is lowered, which reduces the formation of nitrogen oxides therewithin, and consequently, the emission of these oxides within the exhaust gases. There is general agreement that recycling exhaust gases through the inlet manifold is necessary only during intermediate load conditions, when large amounts of nitrogen oxides are generated, while such recycling is practically useless when the engine is idling or operating at full load, when such recycling even has the disadvantage of causing some loss of power. It is necessary therefore to utilize an arrangement for controlling the recirculation of exhaust gases which corresponds to different engine operating conditions.
Arrangements are known for controlling the recirculation of exhaust gases which rely upon a valve within the recirculation path from the exhaust manifold to the inlet manifold of the carburetion system, the obturator of which is caused to open or close by means of a vacuum capsule actuated by means of the vacuum condition prevailing within the main inlet passage of the engine. Also known are means for sensing the vacuum conditions which consist of at least one orifice or slot located within the main intake passage just upstream of the throttle valve so that when the latter is closed, such as for example during idling, such means for sensing the vacuum condition is at atmospheric pressure and will experience a vacuum condition only at intermediate throttle positions, the vacuum becoming too slight within the open position of the throttle, that is, at full load, to act upon the diaphragm of the vacuum capsule of the recirculation system.
The principal disadvantage of these known arrangements is that their sensitivity decreases as engine speed increases, while the temperature within the combustion chambers, and therefore the amount of nitrogen oxides produced, also increases. In addition, with the conventional form of stoppers within the recirculation valve, the control of the gas recirculation is not performed gradually, but to the contrary, the opening and closing of the recirculation path is effected rather abruptly.